A LIN network is a single-wire serial communications protocol that is used in a number of industries, including the automotive industry. Reasons for its widespread use in the automotive industry include its scalability and its cost efficiency, the latter of which is at least partially attributed to the simplicity of Universal Asynchronous Receiver/Transmitter (UART) communication and the low cost of using a single-wire medium.
In general, a single LIN network usually includes a number of “slave nodes” that are periodically and/or intermittently addressed by a “master node.” For example, a LIN network may include a single master node and up to sixteen separate slave nodes, and the slave nodes can be addressed by the master node at any given time and in a manner that requires no arbitration or collision management in the slave node itself. In such LIN networks, particularly where the number of slave nodes is large, current draw in each of the slave nodes can be a concern. This is particularly true in instances where it is an objective to reduce the power consumption and/or operating temperature in the individual slave nodes. In such situations, a combination of hardware and/or software techniques may be implemented to address the current draw issue, which in turn can affect power consumption and operating temperature.
In temperature and/or current sensitive applications, implementing a LIN network can present challenges due to the relatively high current draw of the slave nodes, and more specifically, of the LIN transceivers which are components of the slave nodes. According to the prior art circuit shown in FIG. 1, a typical LIN slave node 10 is connected to a LIN bus 12 and includes LIN transceiver 20, a microcontroller 22, and one or more additional component(s) 24 such as a sensor unit. The LIN transceiver 20 pre-filters and buffers all incoming signals from LIN bus 12, which causes the LIN transceiver to come out of a sleep mode every time there is a request or command placed on the LIN bus, even when it pertains to an entirely different slave node. Because LIN transceiver 20 is not a low current device, this can have a detrimental effect on the overall current being drawn by slave node 10. In certain temperature and/or current sensitive applications, the increased current draw caused by LIN transceiver 20 waking up each time a request is put on LIN bus 12 is undesirable.
An example of such a temperature and/or current sensitive application is disclosed in U.S. Pat. No. 6,422,062, which is assigned to the present assignee and is hereby incorporated by reference. This patent discloses an Integrated Glass Fog Sensor unit (hereafter referred to as an ‘IGFS unit’), and is the type of sensor that could be used as sensor unit 24 in FIG. 1. Of course, the IGFS unit taught in the '062 patent is strictly being provided for exemplary purposes, as a number of other sensors and/or components could also be used in LIN slave node 10. The IGFS unit of this patent has a glass surface temperature sensor, an ambient air temperature sensor and a relative humidity sensor, and is used for predicting glass fog formation on a vehicle windshield.
Thus, it would be advantageous to provide a slave node for use in a LIN network where the slave node has a reduced operating current, power consumption and/or operating temperature. It is also desirable to provide a slave node for use with temperature and/or current sensitive applications such as, but not limited to, an IGFS unit.